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Is there any reason there can't be a photo with a wavelength greater than the width of the (visible) universe? It seems like a photon with a 96 billion lightye
by SomeStupidPoint 9y ago
Is there any reason there can't be a photo with a wavelength greater than the width of the (visible) universe?
It seems like a photon with a 96 billion lightyear wavelength has 2 * 10^-52 Joules of energy. (1 * 10^-33 eV); is there any reason a photon can't have that little energy?
- ars 9y agoAmong other things it would take 96 billion years to create the photon. So that means whatever process created it needs to take that long. I'm not sure what would happen if the process is interrupted before it's complete. But I suspect the photon would "go back in time", and never have been emitted in the first place. This "time travel" doesn't pose issues because the photon takes that long to be detected, so if it's interrupted it simply wouldn't be detected. See also: https://en.wikipedia.org/wiki/Soft_photon https://en.wikipedia.org/wiki/Soft_photon
- SomeStupidPoint 9y agoWouldn't it only take 13 billion years if you'd started at the big bang and a photon that had the wavelength of the then observable universe (since space stretched under it)? I also have to ask how that jives with it being a quantized change: either the photon emits or it doesn't (since a photon exists with that energy or it doesn't) -- or there's some probability distribution that we'll detect the photon (which might change over time) -- but how can it be half emitted 46 billion years in the process? In the end, either it provides a kick at its energy level to another property (eg, electron momentum) in one quantum jump.
- AnimalMuppet 9y agoHmm. In an expanding universe, what's happening to the Planck length? Is it staying constant? Expanding at the rate of expansion of the universe? Doing something else?